The recovery of petroleum oil from subterranean formations, whether on land or in the ocean, produces a substantial amount of water which is mixed with the desired petroleum oil components. This oil-associated water, called "produced water", includes water-insoluble petroleum oil components, such as petroleum oil and grease, generally in amounts less than about 100 parts per million, typically less than about 50 parts per million. The produced water also contains a number of water-soluble petroleum oil components, some of which are more water-soluble than others. The very water-soluble petroleum oil components are not presently regulated by EPA regulations and may be returned to the ocean from an off-shore petroleum oil production facility. Produced water also contains marginally water-soluble petroleum oil components, generally in amounts of about 100 to about 2,000 parts per million, that are the subject of EPA regulations because of their marginal water-solubility.
The very soluble petroleum oil components may be returned to the ocean from an off-shore petroleum oil production facility, since they do not cause any perceivable ocean contamination. The marginally water-soluble petroleum oil components, however, may not be returned to the ocean from an off-shore petroleum oil production facility because these materials have a tendency to separate from ocean water, due to the relatively low ocean water temperature, and agglomerate in the form of suspended droplets that result in a sheen on the surface of the ocean. Presently, these marginally water-soluble petroleum oil components cannot be returned to the ocean in a concentration greater than 29 parts per million.
It is well known that water-soluble organic materials can be removed from liquid and gas streams by contacting these streams with an adsorbent resin, such as an ion-exchange resin, in batch or continuous processes. Such ion-exchange resins have been used for the purpose of removing the marginally water-soluble petroleum oil contaminants from produced water, i.e., the macroreticular ion-exchange resins disclosed in U.S. Pat. Nos. 5,104,545 and 5,135,656, hereby incorporated by reference. As set forth in more detail in these two patents, various techniques have been developed for removal of oil and water-soluble organics from produced water, and these known processes suffer from the disadvantages of requiring the addition of chlorinated hydrocarbon solvents and/or strong acids and/or mixing the produced water with crude oil in order to separate the water-soluble organics from the produced water.
The use of the macroreticular bead ion-exchange resins disclosed in the '545 and '656 patents has the advantage of not requiring chemical addition to the produced water for the purpose of adjusting the pH of the produced water in order to remove the water-soluble organic contaminants. However, commercially, the macroreticular bead ion-exchange resins have not been feasible due to the produced water containing a substantial quantity, i.e., 10-100 parts per million, of water-insoluble oil. Oil or grease conveyed into a bed of ion-exchange resin beads quickly fowls the resin beads such that a maximum of only about 10-20 bed volumes of the oil-contaminated water can be passed through the beads before it is necessary to regenerate the resin beads.
Such macroreticular resin beads, such as a terpolymer of styrene-divinylbenzene-ethyl-vinylbenzene, also have been used to remove water-immiscible oil components from water, as disclosed in Canadian Patent No. 1,103,170. However, in order to remove the oil, it is necessary to add an emulsifying agent to the oil-contaminated water, and also necessary to add a strong acid to acidify the surfactant and lower the pH to about 2-6, usually to about 3 to provide oil/water phase separation. Further, frequent regeneration of the resin beads is necessary, generally after about every two bed volumes of oil-contaminated water is passed through the macroreticular resin bead bed.